Methods, systems and devices for generating subsonic pressure waves in intravascular lithotripsy

ABSTRACT

Various embodiments of the systems, methods and devices are provided for breaking up calcified lesions in an anatomical conduit. More specifically, an electrical arc is generated between two spaced-apart electrodes disposed within a fluid-filled balloon, creating a subsonic pressure wave. In some embodiments, the electrodes comprise a plurality of points that allow the electrical arc to form at any one of the plurality of points to, among other things, extend the electrode life.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 17/449,883,filed Oct. 4, 2021 and entitled SYSTEMS, DEVICES AND METHODS FORGENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY andfurther claims the benefit of U.S. Provisional Patent Application Ser.No. 63/229,737, filed Aug. 5, 2021, entitled SYSTEMS, DEVICES ANDMETHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULARLITHOTRIPSY, the entire contents of which are incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH DEVELOPMENT

None

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to systems, devices and methods for breaking upcalcified lesions in an anatomical conduit. More specifically, anelectrical arc is generated between two electrodes disposed within afluid-filled balloon, creating a subsonic pressure wave.

Description of the Related Art

A variety of techniques and instruments have been developed for use inthe removal or repair of tissue in arteries and similar bodypassageways, including removal and/or cracking of calcified lesionswithin the passageway and/or formed within the wall defining thepassageway. A frequent objective of such techniques and instruments isthe removal of atherosclerotic plaque in a patient's arteries.Atherosclerosis is characterized by the buildup of fatty deposits(atheromas) in the intimal layer (i.e., under the endothelium) of apatient's blood vessels. Very often over time what initially isdeposited as relatively soft, cholesterol-rich atheromatous materialhardens into a calcified atherosclerotic plaque, often within the vesselwall. Such atheromas restrict the flow of blood, cause the vessel to beless compliant than normal, and therefore often are referred to asstenotic lesions or stenoses, the blocking material being referred to asstenotic material. If left untreated, such stenoses can cause angina,hypertension, myocardial infarction, strokes and the like.

Angioplasty, or balloon angioplasty, is an endovascular procedure totreat by widening narrowed or obstructed arteries or veins, typically totreat arterial atherosclerosis. A collapsed balloon is typically passedthrough a pre-positioned catheter and over a guide wire into thenarrowed occlusion and then inflated to a fixed size. The balloon forcesexpansion of the occlusion within the vessel and the surroundingmuscular wall until the occlusion yields from the radial force appliedby the expanding balloon, opening up the blood vessel with a lumen innerdiameter that is similar to the native vessel in the occlusion area and,thereby, improving blood flow.

The angioplasty procedure presents some risks and complications,including but not limited to: arterial rupture or other damage to thevessel wall tissue from over-inflation of the balloon catheter, the useof an inappropriately large or stiff balloon, the presence of acalcified target vessel; and/or hematoma or pseudoaneurysm formation atthe access site. Generally, the pressures produced by traditionalballoon angioplasty systems is in the range of 10-15 atm, but pressuresmay at times be higher. As described above, the primary problem withknown angioplasty systems and methods is that the occlusion yields overa relatively short time period at high stress and strain rate, oftenresulting in damage or dissection of the conduit, e.g., blood vessel,wall tissue.

Shockwave Medical, Inc., markets an alternative to traditionalrelatively high pressure balloon angioplasty. The Shockwave Medical,Inc., intravascular lithotripsy system generates “shock waves” within afluid-filled balloon. Shockwave Medical claims that generated “shockwaves” travel at supersonic speed through the balloon fluid, through theballoon material to interact with the vessel wall tissue, stenosisand/or calcification. The Shockwave Medical, Inc., system requires arelatively close spacing between electrodes in an electrode pair whereinthe spark gap is disposed. Shockwave Medical's currently known systemsprovides relatively small axial coverage of lesions. The structure ofShockwave Medical's electrode pairs thus requires additional electrodepairs spaced apart axially from each other and/or a translatable,slidable electrode pair carrier that may be used to translate theelectrode pair(s) to better cover an elongated lesion.

Various embodiments of the present invention address these issues, amongothers, discussed above.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These drawings are exemplary illustrations of certain embodiments and,as such, are not intended to limit the disclosure.

FIG. 1 illustrates a perspective and partial cutaway view of a distalregion of one embodiment of the present invention.

FIG. 2 illustrates a perspective view of a distal region of oneembodiment of the present invention.

FIG. 3 illustrates a perspective view of a distal region of oneembodiment of the present invention.

FIG. 4 illustrates a side, cutaway view of a distal region of oneembodiment of the present invention.

FIG. 5 illustrates a perspective, cutaway view of a portion of a distalregion of one embodiment of the present invention.

FIG. 6 illustrates a side cutaway view of a portion of a distal regionof one embodiment of the present invention.

FIG. 7 illustrates a perspective, cutaway view of a portion of a distalregion of one embodiment of the present invention.

FIG. 8 illustrates a perspective, cutaway view of a portion of a distalregion of one embodiment of the present invention.

FIG. 9 illustrates perspective views of ring electrodes of oneembodiment of the present invention.

FIG. 10 illustrates a side cutaway view of two intermediary electrodeswith an operative electrical communication therebetween.

FIG. 11 illustrates a side cutaway view of two intermediary electrodeswith an operative electrical communication therebetween.

FIG. 12 illustrates a side cutaway view of two intermediary electrodeswith an operative electrical communication therebetween.

FIG. 13 illustrates a side view of simultaneous arcs and a side viewwith one arc delayed relative to the other arc.

DETAILED DESCRIPTION OF THE INVENTION

Generally, embodiments of the present invention comprises methods anddevices for generating subsonic waves for disrupting or crackingcalcified regions within a blood vessel, though the disruptive effectsof the generated subsonic waves may extend to partially or non-calcifiedoccluding material. More specifically, with reference to the Figures, anexemplary embodiment 100 comprises an elongated member or carrier 102such as a catheter with a known inflatable angioplasty balloon 104mounted on or near the distal end 103 of the elongated carrier 102 whichin certain embodiments may comprise a laser cut polyimide tube. Thedistal end 105 of the balloon 104 may be sealed against or around theelongated carrier 102 to create a watertight barrier and furthercomprises a fluid inflating/deflating channel 106 in fluid communicationwith the interior of the balloon 104 and in fluid communication with afluid-containing reservoir (not shown) that is located external to thepatient, and as is well-known in the art, for inflating the balloon 104with fluid F and deflating balloon 104. A guide wire lumen (not shownbut as is well-known in the art) configured to allow translation of aguide wire extends through the elongated carrier and distally outtherefrom, an arrangement also well known to the skilled artisan.

It is to be understood that the various embodiments of the presentinvention are also effective within a fluid-filled environment, e.g., abodily cavity and/or a blood vessel, i.e., without requiring afluid-filled balloon. The various embodiments are described in relationto a fluid-filled balloon, but will also apply to an elongated catheterdisposed within a fluid-filled environment wherein the subsonic pressurewave generators described infra may be disposed along the elongatedcarrier within the fluid-filled environment. All such embodiments arewithin the scope of the present invention.

Therefore, at least one subsonic pressure wave generator 200 isprovided, wherein each subsonic pressure wave generator comprises aproximal ring electrode and a distal ring electrode, with a spark gapdefined therebetween. In some embodiments, two subsonic pressure wavegenerators 200, 200′ may be provided. In still other embodiments, morethan one subsonic pressure wave generator, i.e., two or more, may beprovided.

As referred to herein, subsonic pressure wave generator is defined as amechanism that, when actuated, generates a wave(s) of energy within afluid-filled environment such as an angioplasty balloon. The generatedwave(s) thus travel through the balloon material at subsonic speed andalso interact with tissue and/or calcified material located outside ofthe balloon at subsonic speed. In other words, the wave(s) generated bythe subsonic pressure wave generators do not travel through the balloonmaterial or impact tissue or calcified material outside of the balloonat the speed of sound or greater. Further, the term “wave” is notintended to be limiting to a “wave” per se. Instead, a traveling frontof energy is generated and that moves through the fluid within theballoon, generally away from the subsonic pressure wave generator fromwhich it eminates. This traveling front of energy may comprise asymmetrical expansion shape around the elongated catheter 102, or mayexpand and travel in an asymmetric shape relative to the elongatedcatheter 102. In each embodiment, the traveling front of energy, i.e.,the “wave” as referred to herein, travels through the balloon materialand impacts materials outside of the balloon at subsonic speeds.

Alternatively, the subsonic pressure wave generator may comprise aresistive heater or a pulse heater as is known in the art.

If a single subsonic pressure wave generator 200 is provided, it may besubstantially axially centered within the balloon 104. In otherembodiments, the single subsonic pressure wave generator 200 may bebiased to the proximal or to the distal end of the balloon's interior.

When two or more subsonic pressure wave generators are provided, 200,200′, adjacent subsonic pressure wave generators, e.g., 200, 200′, maybe spaced axially apart from each other, wherein the resultant sparkgaps defined by each subsonic pressure wave generator 200, 200′, areaxially spaced apart from each other. In cases wherein three or moresubsonic pressure wave generators are provided, the resultant spark gapbetween adjacent subsonic pressure wave generators may be substantiallyequal, or one or more spark gaps may be longer or shorter than othersubsonic pressure wave generators.

As further seen in the Figures, a first, proximal, subsonic pressurewave generator 200 may comprise a proximal ring electrode 201 and anaxially spaced apart distal ring electrode 202, defining a spark gaptherebetween. Next, a second, more distal, subsonic pressure wavegenerator 200′ may comprise a proximal ring electrode 203 and an axiallyspaced apart distal ring electrode 204, also defining a spark gaptherebetween. As will be discussed further, the distal ring electrode202 of subsonic pressure wave generator 200 and the proximal ringelectrode 203 of subsonic pressure wave generator 200′ may be inelectrical communication with each other to enable current to flowtherebetween.

As will be understood by skilled artisan, the electrical communicationmay be effectively reversed. First, e.g., with a proximal electrodeelectrically coupled or in electrical communication with a “high” powerside of a circuit and pulse generator connected therein, and a distalelectrode electrically coupled or in electrical communication with a“ground” or “return” side of the circuit and pulse generator connectedtherein. Second, a distal electrode may be electrically coupled or inelectrical communication with a “high” power side of a circuit and pulsegenerator while a proximal electrode may be electrically coupled or inelectrical communication with a ground or return side of the circuit andpulse generator. In either case, once the subsonic pressure wavegenerator(s) is/are actuated, the circuit is completed and current willflow through the circuit.

At least one of the subsonic pressure wave generators, e.g., 200 may bein direct electrical connection and communication with an externallylocated power source or pulse generator 300, wherein the pulse generatormay be configured to provide voltage pulses of a predetermined magnitudeand pulse length along an electrical conductor to a proximal ringelectrode of a proximal-most subsonic pressure wave generator 200.Alternatively, the voltage pulses may be delivered without apredetermined magnitude or pulse length. In some embodiments, acollapsing field in an inductor, e.g., a well-known car ignitionmechanism), or decaying voltage from a capacitor may be employed,neither of which comprise or require a predetermined voltage or pulselength.

Each subsonic pressure wave generator 200, 200′, etc., comprises a pairof axially spaced-apart ring electrodes. Electrode pairs 201, 202 and203, 204 are shown in axially spaced-apart disposition and mountedaround the elongated carrier 102, e.g., by crimping or other attachmentmeans and are immersed within the fluid F in the inflated balloon 104.Accordingly, spark gaps are defined between electrode pair 201 and 202,and between electrode pair 203 and 204, wherein electrodes 202 and 203are in operative electrical communication or connection. As discussedabove, the spark gaps may be of equivalent length or may comprisediffering lengths. In some embodiments, a single subsonic pressure wavegenerator 200 may be provided, while in other embodiments, more than onesubsonic pressure wave generator 200, 200′, etc., may be provided.

Thus, in some embodiments, first and proximal-most ring electrode 201may be electrically coupled or in electrical communication orconnection, via an electrical conductor, with a power source, e.g., thepulse generator 300, that is configured for supplying voltage pulses tothe electrode pair(s) comprising the subsonic pressure wave generator(s)200. The distal-most ring electrode, e.g., 204, may also be electricallycoupled or in electrical communication or connection, via a secondelectrical conductor, with the power source, e.g., pulse generator 300.

The fluid F within the inflated balloon 104 is ionically conductive,e.g., saline, to facilitate arcs, or current flow, between thespaced-apart ring electrodes in each electrode pair 201, 202 and 203,204 comprising the subsonic pressure wave generators 200 and 200′. Thus,upon application of sufficient voltage generated by the pulse generator300 to the proximal-most electrode, e.g., 201, via a conductor inelectrical connection or communication between pulse generator 300 andelectrode 201, may cause current to flow between electrode 201 andelectrode 202 and wherein an arc is generated across the defined sparkgap between electrodes 201, 202. A return conductor in operativeelectrical connection or communication with electrode 202 completes thecircuit back to the pulse generator 300. In this manner, the circuit maycomplete or close during the arcing between ring electrodes 201, 202 inan embodiment having a single electrode pair comprising a singlesubsonic pressure wave generator 200.

It is known that current can flow between the electrodes without an arc.Current generally flows in an electrolyte by ion diffusion. An arc orspark is present when electrons or ions can accelerate past theionization energies of the local molecule, creating a cascade. Often,this is a plasma and may occur through the bulk fluid, e.g., theconducting fluid F, but is more likely to occur along a fluid-surfaceinterface, e.g., along the outer surface of the catheter 102. Theseconditions may also result in generation of subsonic pressure waves asdescribed above.

In an embodiment comprising more than one subsonic pressure wavegenerator 200, 200′ such as illustrated, upon application of sufficientvoltage by the pulse generator 300, the current flow (arcing) mayproceed from electrode 201 to electrode 202 across the defined spark gaptherebetween. Next, electrode 202, being in operative electricalcommunication with electrode 203, enables current to flow from electrode202 to electrode 203 which, in turn, results in current flow fromelectrode 203 to electrode 204, across the spark gap definedtherebetween. A return conductor in operative communication withelectrode 204 completes the circuit back to the pulse generator 300.

The flow discussed above comprises a “current” passing from electrode201 to 202 is initially ion diffusion as discussed above (before the arcis established), followed by streamers initiating from one or morepoints 206 of electrode 201, followed by plasma channels being formedeither through the fluid F and/or at, or along, the fluid F surfaceinterface. The fluid F surface interface may comprise the outer surfaceof catheter 102 and/or the inner surface of angioplasty balloon 104.

FIG. 1 illustrates the fluid-filled balloon 104 in an inflated statewherein a conductive fluid F such as saline fills the balloon's interiorspace, with the spaced-apart ring electrodes 201, 202 and 203, 204disposed therein and immersed in fluid F. Electrodes 201, 202, 203 and204 are arranged generally symmetrically around the elongated carrier102 and generally symmetrically along a center line of the inflatedballoon 104. However, in a preferred embodiment, as shown in at least.FIG. 6 , a channel 208 may be defined through or along the ringelectrodes along a longitudinal plane to allow the insulatedconductor(s) to be disposed at least partially therein so as to reducecrossing profile of the system. Thus, the channel 208 may be formed bycarving out a portion of ring electrode wherein the ring electrode doesextend circumferentially around the elongated carrier 102.Alternatively, as illustrated in FIG. 6 , channel 208 may comprise avoid or space between two spaced-apart ends of the ring electrode,wherein the ring electrode extends partially circumferentially aroundthe elongated carrier 102 and wherein the conductor may extend along theouter surface of elongated carrier 102. With the exception of theinterruption of the channel 208 in the ring electrode(s), the preferredstructure is symmetrical as discussed above, though asymmetricalelectrode(s) may also be employed.

FIGS. 2-12 illustrate possible arrangements and embodiments of thespaced-apart ring electrodes that form each electrode pair as well asthe conductive wire connections thereto.

FIG. 2 thus illustrates the elongated carrier 102, which may comprise alaser cut tube and may comprise polyimide or other material. Twoexemplary subsonic pressure wave generators 200, 200′ are shown inaxially spaced-apart relation relative to each other along the elongatedcarrier 102. Each subsonic pressure wave generator, e.g., 200, 200′,comprise spaced-apart exemplary ring electrodes, respectively 201, 202and 203, 204, each defining a spark gap between the relevantspaced-apart ring electrodes of a predetermined length, that is thespacing distance between the spaced-apart ring electrodes 201 to 202,and 203 to 204. The distal ring electrode, e.g., 202, of the proximalsubsonic pressure wave generator 200 and the proximal ring electrode 203of the distal subsonic pressure wave generator 200′ are shown inrelatively close disposition forming an interface I therebetween, theinterface defining and comprising an electrical communication betweenthe two ring electrodes defining the interface I.

The various forms and types of electrical connections between theseintermediary ring electrodes 202, 203 defining an interface I aredescribed further herein, but generally comprise a physical or operativeelectrical connection between surfaces of the two intermediary ringelectrodes that may comprise a touching relationship, a weld bead, or ajumper wire or other conductive interconnection element, or mechanism,between the two intermediary ring electrodes 202, 203, or otherconducting connection. The skilled artisan will readily recognizealternative mechanisms for creating the required electrical connectionbetween the intermediary ring electrodes, 202, 203 i.e., betweenadjacent subsonic pressure wave generators 200, 200′, each of which iswithin the scope of the present invention. In this arrangement, the twoor more subsonic pressure wave generators 200, 200′, etc., may beelectrically connected in what effectively becomes a series circuit. Thenumber of subsonic pressure wave generators used in certain embodimentsmay be one, or two, or more than two.

As discussed further herein, the ring electrodes described herein areexemplary, other electrodes shapes and structures are within the scopeof the present invention. In certain embodiments, and as discussedfurther herein, at least one of the electrodes in an electrode paircomprising a subsonic pressure wave generator may comprise a pluralityof points or extensions that extend toward the spark gap defined betweenthe electrode pair.

Still further, certain embodiments may comprise a plurality of electrodepairs, at least one electrode pair comprising a proximal-most ringelectrode in wired, or other, electrical communication with the pulsegenerator 300. In some embodiments, more than one electrode pair in theplurality may comprise a proximal-most ring electrode in wired, orother, electrical communication with the pulse generator 300, wherein atleast one of the electrode pairs in the plurality may be separately andindividually energized by the pulse generator 300. Thus, certainembodiments may comprise a parallel connection arrangement of at leastsome electrode pairs, or may comprise a combination of series connectedsets of electrode pairs with one or more sets of electrode pairscomprising a parallel connection back to pulse generator.

The skilled artisan will recognize that the reference to an operativeelectrical connection or communication with a proximal-most ringelectrode of an electrode pair and the pulse generator 300 is merelyillustrative. It is within the scope of the present invention to simplyswitch the operative electrical connection to be between a distal-mostring electrode of an electrode pair and the pulse generator 300.

In certain configurations, individual subsonic pressure wave generators,200, 200′ may be controlled regarding the magnitude of voltage applied,the magnitude of current flow resulting in an arc between the ringelectrodes comprising the subsonic pressure wave generators, the timeduration of current flow and arcing between the ring electrodescomprising the subsonic pressure wave generators, the current in theprimary of a discharge inductor, the charge in a discharge capacitorand/or the initiation time of the current flow or arcing between thering electrodes comprising the subsonic pressure wave generators.

For example, and with reference now to FIG. 13 and application of therelated detailed description infra, is possible to axially translate orshift a central node between generated pressure waves by slightlydelaying generation of one pressure wave by one or more adjacentsubsonic pressure wave generators, e.g., 200 or 200′, relative to thetiming of generation of a pressure wave by an adjacent subsonic pressurewave generator, such variable gap spacing may also provide analternative, or supplemental, mechanism for moving the resultingpressure waves, and nodes disposed therebetween, axially along thecatheter 102 within balloon 104. The delay in pressure wave generationmay be used alone, or in combination with the axial spacingdifferentials between adjacent subsonic pressure wave generators 200,200′.

As shown in FIG. 13 , two (or more) pairs of ring electrodes, 201/202and 203/204 may be provided within the fluid-filled balloon. The arcingfor each pair 201/202 and 203/204 may be generated substantiallysimultaneously, resulting in equal-sized bubbles at any given time andsubsonic pressure waves P with a central node C generally in the middleof the generated subsonic pressure waves P.

Alternatively, one arc (and resultant subsonic pressure wave P) may beslightly delayed which is used to shift the central node C proximally ordistally to enable treating along the axial length of the balloon. FIG.13 illustrates the axial offset Δ of the central node C vs C′ as aresult of this delay technique. Such a delay in arcing, and resultingsubsonic pressure wave P′ which is slightly delayed relative to subsonicpressure wave P, may be timed and used to create a sweeping effect of aaxially translating pressure wave through the length of the balloon andalong the length of the lesion. A processor may be provided aswell-known in the art to execute a pre-programmed set of instructionscomprising various timing sequences of the pulses and resulting arcs andpressure waves to optimize focus of the waves including, but not limitedto sweeping the lesion in axial directions. As shown, the pairs ofinteracting ring electrodes 201/202 and 203/204 are adjacent each otheralong the elongated carrier. In other embodiments, non-adjacent ringelectrode pairs may interact as discussed above.

Catheter and Electrodes

As provided above, an exemplary laser-etched polyimide tube 102 may beprovided with ring electrodes 201, 202 and 203, 204, wherein the ringelectrodes are crimped around the tube, with insulated wires connectingthe ring electrodes back to the external pulse generator 300.

In the two-wire configuration shown, the gap between the electrodes maybe decreased by opening the distance between the two adjacent center,intermediary electrodes (202 and 203) in the electrode pairs whileelectrically connecting them with an additional wire.

FIG. 9 provides an exemplary ring electrode E having a body portion Bdefining a central aperture A configured to securely engage the catheter102, channel 208, a front surface defining a plurality of points 206 anda flat rear surface. Points 206′ illustrate exemplary effects ofcorrosion on one of the points caused by arcing between adjacent ringelectrodes. One or more of the remaining points 206 may engage togenerate the arc across the spark gap.

The points 206 may comprise a substantially triangular profile asillustrated. However, other profiles are also contemplated. Theunderlying functionality of the points 206 is to enable arcs to initiatefrom different locations on the electrode. Therefore, any shape thatextends away from the main body of the electrode generally toward thedistal-most electrode in an electrode pair, and generally toward thespark gap defined therebetween, comprising a subsonic pressure wavegenerator will be sufficient. The tip regions of adjacent ones of theplurality of points are in certain embodiments, spaced apart from eachother.

Multiple points 206 on the exemplary ring electrodes facing the sparkgap region defined between ring electrodes, 201, 202, allow electricalbreakdown streamers to initiate from several different locations orpoints 206 disposed on and/or around the ring electrode, so viablepoints 206 remain when some are corroded by the arc. This extends theeffectiveness and life of the ring electrode. In addition, the path ofthe arc may comprise debris, so originating arcs from differentlocations, i.e., points 206, on the electrode(s) aids in reducing thedebris, making it less likely that a short is formed. In this way, theenvironment surrounding the electrodes and within the spark gaptherebetween is maintained as uniformly as possible throughout thetreatment session comprising a plurality of pulses.

Accordingly, as illustrated in the Figures, and as the skilled artisanwill readily understand, the uncorroded point(s) 206 involved inelectrical arcs, begin to corrode as electrical arcing proceeds. Asshown in FIGS. 5 and 9 , points 206 corrode to shorten to form degradedor corroded points 206′. In turn, as will be understood and illustrated,the spark gap between corroding, or corroded, points 206′ will lengthen,creating a greater length of fluid and distance, and resistance,therebetween. Thus, the current flow streamers may continually seek outa shorter, less resistant, spark gap formed or defined by, or betweenone or more uncorroded points 206 that are longer in length thatcorroded point(s) 206′. Relatedly, in some embodiments, as best shown inFIG. 5 , one or more of the uncorroded points 206 may have a length thatis longer than one or more of the other points 206, as measured by thepoint(s) 206 relative length of extension toward the spark gap. Thelonger point(s) 206 thus comprise a spark gap length that is shorter,and less resistant, than the spark gap length of other point(s) 206 thatare shorter, or the spark gap length of points 206′ that are corrodedand, therefore, shortened to define a longer spark gap lengththerebetween. FIG. 5 shows an exemplary set of points 206 wherein onepoint 206 is “longer” than an adjacent “shorter” point 206 and a stillshorter point 206′ that has been shortened by corrosion by electricalarcing. As the skilled artisan will readily understand, current flowstreamers may preferably seek out a shorter, less resistant, spark gap,i.e., a spark gap comprising one or more “longer” points 206.

The electrodes, including exemplary ring electrodes 201, 202, 203, 204,may be metal or semiconductor, and can be plated with a secondary alloy.The base metal may comprise copper or beryllium copper. The plating maycomprise platinum, gold, tungsten, osmium, silver, nickel, or otherelectrochemically low-activity metal. Carbon surfaces such as graphite,graphene, and diamond may also be used. Still further, stainless steeland steel alloys may be used.

The connection between electrode pairs, e.g., 201, 202 and 203, 204, maybe achieved in many embodiments. As discussed above and as shown in FIG.10 , in one embodiment, the two intermediary ring electrodes, e.g., 202and 203, may be placed in a physically touching relationship wherein theelectrical connection effectively comprises a short between the touchingelectrodes 202, 203, allowing current to flow therebetween. Theelectrode rings 201, 202, 203, 204 may comprise a rear surface (shown inFIG. 9 ) that, may be substantially flattened, wherein the rear surfacesof intermediary ring electrodes 202, 203 may be in a physically touchingengagement, Alternatively, the rear surfaces of exemplary intermediaryring electrodes 202, 203 may be spaced apart as further discussed here.Still more alternatively, the rear surfaces of the intermediary ringelectrodes may comprise complementary shapes, e.g., one convex and theother concave, wherein one rear surface fits within the other rearsurface to comprise a fuller physically touching engagement between theintermediary ring electrodes, e.g., 202, 203. The rear surface which maybe relatively flattened comprises the side opposite the plurality ofpoints 206 which form and define a front surface of each exemplary ringelectrode 201, 202, 203 and 204.

As shown in FIG. 12 , rear surfaces of intermediary electrodes 202, 203may be configured in an adjacent but spaced, apart and non-touchingengagement, wherein a jumper conductive wire is disposed between theintermediary electrodes 202, 203 across interface I, or, as in FIG. 11 ,a welded bead interconnects the electrodes 202, 203 at the interface I.Alternative means to achieve the required electrical connection at theinterface I between intermediary ring electrodes 202, 203 may appear tothe skilled artisan, each such electrical connection means is within thescope of the present invention.

Alternative electrode embodiments comprise at least some non-ringelectrodes attached or mounted or connected with the elongated catheter102, wherein pairs of the non-ring electrodes are arranged inspaced-apart configurations to form subsonic pressure wave generators asdescribed above in connection with the ring electrode embodiments. Ringand non-ring electrodes may be combined in a given system.

Still more alternatively, at least some of the electrodes may bedisposed along the inner surface of the balloon 104. In certainembodiments a proximal electrode, e.g., a ring electrode such as 201 maybe provided and mounted on or along catheter 102, and paired with anelectrode disposed along the inner surface of balloon 104. As voltagepulses are applied, an arc may generate between the catheter-mountedelectrode and the balloon-mounted electrode, generating in turn subsonicpressure wave(s). Still further, a distal catheter-mounted electrode,e.g., ring electrode 202, may be spaced away from both the proximalcatheter-mounted electrode and from the balloon-mounted electrode. Inthis embodiment, a first subsonic pressure wave may result from an arcbetween the proximal catheter-mounted electrode and the balloon-mountedelectrode. A second subsonic pressure wave may then result from an arcbetween the balloon-mounted electrode and the distal catheter-mountedelectrode. A heat shield may be disposed along and/or around the regionwhere the balloon-mounted electrode is positioned to aid in heatdissipation and conduction of generated heat away from the balloonmaterial.

Finally, the subsonic pressure wave generators may all be mounted alongthe inner surface of the balloon, with arcs and resulting subsonicpressure wave generation as described herein.

Electrodes mounted on the inner balloon surface may comprise a carbonfilament in operative communication with a pulse generator and which mayalso affect, e.g., limit, the expansion radius of the balloon.

In all of the cases, a plurality of points 206 may be provided on atleast one of the electrodes in an electrode pair comprising a subsonicpressure wave generator.

The plurality of points 206 will also help in cases where the elongatedcatheter 102 is in a curved disposition due to the tortuosity of thesubject vessel. In this situation, the points 206 of the subjectelectrodes in an electrode pair that are on an inner radius of thecurved catheter 102 are in closer proximity to each other than thepoints 206 on an outer or intermediary radius. Thus, these points 206that are in closer/closest proximity will be likely to generate the arcand resultant subsonic pressure wave.

Further, it is possible to create a preformed curvature in the catheter102 in order to effectively select which points 206 are likely togenerate the arc and resulting subsonic pressure wave. Such a preformedcurvature may be built into the catheter 102 using a mandrel and heatsetting or other known techniques and/or shaping metal alloys such asNitinol. One of more of these preformed curvature region(s) may belocated along the section inside the balloon 104. This deformation orcurvature may be straightened by translation over the guide wire, andsubsequent withdrawal of the guide wire allows the subject preformedcurvature region to successively move from a deformed straightenedconfiguration to a non-deformed and curved configuration. As will now beapparent, more than one of these preformed curved regions may beprovided within the balloon and may be positioned adjacent toelectrodes, within or along electrode pairs and/or subsonic pressurewave generators. The preformed curved regions may Like curved excursionpaths that are in a same direction, or in different directions and maybe interposed with straight non-curved sections. In this way, theoperator may effectively change the direction of the pressure wave tocreate more effective disruption of the targeted region.

In certain embodiments, individual points 206 may be specificallyenergized with individual wired connection(s) and/or individual points206 may be de-energized in order to ensure they do not participate incurrent flow, for at least a period of time and/or during treatment of acertain region of the subject vessel.

In other embodiments, the points 206 may be selectively andintentionally degraded (or not degraded) based on material selectionand/or relative length of the tip of certain of the points 206 relativeto the other points 206.

Wiring/Cabling

The disposable catheter assembly may comprise two or more insulatedconductors connecting the system of electrodes, electrode pair(s) and/orsubsonic pressure wave generator(s) to the power supply. A typicalexcitation pulse is 50A√2KV for 5 usec, requiring a load impedance of 40ohms, The round trip cable length in the disposable catheter isapproximately 10 feet, so the maximum resistance of the cable is 2ohms/foot for each trace.

Twisted wire pairs may form transmission lines whose characteristicschange with the wire diameter and spacing. If, for example, 40 ga copperwire is spaced 0.25 mm (10 mils) apart (for 5 mil thick insulation), thetwisted wire pair may form a 1.1 uH inductor which may, in turn, causethe rise time of an ideal 50A 2KV source to be about 25 nsec.Alternatively, larger, more conductive wire may be used and a resistancemay be added to the circuit to accommodate the ideal resistance in thesystem.

The Figures illustrate electrical conductors comprising insulation thatare operatively connected with the pulse generator 300 and wherein oneof the electrical conductors is in electrical communication with theproximal-most ring electrode 201, an electrical structure well-known tothe artisan. FIG. 4 provides an exemplary connection embodiment whereina distal end of conductor is stripped of insulation exposing a length ofdistal conductor portion 212 that is operatively connected with ringelectrode 201. A similar connection mechanism may be employed for theconnection between the other electrical conductor and the distal-mostring electrode, e.g., element 204.

Alternatively, a conductor may comprise a distal conductor portion 214that is stripped of insulation and that is connected with the relevantring electrode by a weld bead 216 as shown in FIG. 8 . Any of theelectrical conductors may be connected to the relevant, ring electrodein this manner.

In order to minimize outer diameter and crossing profile of the system,the electrical conductors may be run within a lumen defined in catheter102, wherein the distal conductor portion is operatively connected withthe relevant ring electrode through an aperture in the catheter 102and/or via a weld head as described above.

Alternatively and as shown in the Figures, the ring electrodes 201, 202,203, 204, may comprise a channel 208 sized for the electricalconductor(s) to reside within. The channel 208 may provide theconnection point for one or more of the ring electrodes as is shown in,e.g., FIG. 8 . Channel 208 may allow the electrical conductor(s) toslide there along to accommodate changes in the attitude of the catheter102 during advancement of the device 100 through a patient'svasculature.

Still more alternatively, a longitudinal channel or a spiral or othershaped channel may be defined in the wall of elongated catheter 102. Theconductor(s) may be at least partially disposed in the channel to assistin minimizing crossing profile of the system.

Power Supply/Pulse Generator

In some embodiments, a capacitor bank may be provided and may be chargedduring an exemplary 1-minute off period, followed by a short orconnection of the capacitors to the electrodes for the discharge and arcgeneration. The charging period may be less than 1-minute in preferredembodiments. In other embodiments, a current may be established in atransformer primary, wherein that current is halted to generate a largevoltage across the secondary.

As noted, the charging period may be much less than 1 minute as a pulsemay be delivered to the electrodes at least once a second. The pulserate may be limited with sensed temperature of the conductive fluid Fand/or balloon material so that the temperature of surrounding tissue isnot increased beyond a predetermined threshold, e.g., 1 degree C. oftemperature increase for cardiac tissue. The temperature may bemonitored using a temperature sensor mounted along the outside surfaceof the catheter 102 within the conductive fluid F and/or on an innersurface of the balloon, or other location. The temperature sensor may bein operative communication with an externally located processor havingoperational communication with the predetermined heat threshold(s) andwherein an alert is provided via a display or other mean. In someembodiments, the voltage pulses may be locked out, with no furtherpulses allowed. In other embodiments, no further voltage pulses areallowed when the predetermined heat threshold is met or exceeded, butthe voltage pulses may proceed when the sensed temperature drops belowthe predetermined heat threshold.

The capacitor bank may be charged from either direction and FETs arecontrolled to allow the capacitor banks to discharge between theelectrodes in an H-bridge configuration. In some embodiments, thecurrent sign may be configured to flip. Phase shaping may be executed toreduce EMI in some embodiments. In some embodiments, both the currentand voltage may be monitored to inform what the voltage setting shouldbe for the next pulse delivery. In some embodiments, the voltage may beterminated on a pulse-by-pulse basis and in other embodiments thevoltage is not terminated on a pulse-by-pulse basis. Similarly, theelectrical arc across a given set of electrodes comprising a subsonicpressure wave generator may be terminated on a pulse-by-pulse basis insome embodiments, while in other embodiments, said electrical arc maynot be terminated on a pulse-by-pulse basis.

Because the treatment scales with the cube root of the deposited energy,casual control of voltage and current suffices. The current may flipsign between pulses, droop or exponentially decay during the pulse, andring or oscillate during the pulse. It is most efficient that theelectrical energy be delivered to the electrodes comprising the subsonicpressure wave generator(s) while the balloon fluid F comprises a massdensity that is relatively high, roughly in the first 1-20 usec.

The current and voltage output may be monitored for proper operation.Measuring opens or shorts may produce a prompt or alert to change acatheter assembly for a new catheter assembly. Monitoring the DCimpedance between the electrodes, e.g., 201 and 202, and the patientallows catheter insulation leaks to be sensed and corrected. As furtherdescribed herein, monitoring the DC resistance between the electrodesmay provide a temperature monitor. Still further, if the vessel issuccessfully being opened by treatment, the DC resistance between theelectrodes decreases because of the larger cross section of salineconducting between the electrodes. It is further understood that as gasis produced from the arcs, the resistance will change.

Further, sensing and/or monitoring the conductivity of the conductingfluid F within the balloon alone, or comparing same with theconductivity of fluid, e.g., blood, outside of the balloon providesalternative mechanisms for determining whether the balloon has beencompromised, e.g., a rupture or tear.

The patient's heart rhythm may be monitored, and that these pulses aresynchronized to an inactive phase. That synchronization precludes somestandard methods, such as a spark gap that closes when the capacitorbank reaches a target voltage. Relatedly, the balloon 104 will expandand contract with a characteristic time and frequency. Voltage pulsesmay be timed to take advantage of the natural expansion/contractioncycle and frequency. For example, voltage pulses may be timed to thenatural expansion of the balloon and/or to the natural contraction ofthe balloon. The force of the subsonic pressure waves will impact thetarget tissue and/or occluding material, e.g., calcification, atslightly different angles depending on the balloon's expansion state,because, inter alia, the subsonic pressure wave generators position willchange with expansion/contraction of the balloon.

Temperature Sensor

As discussed above, certain embodiments may comprise a small temperaturesensor embedded near the electrodes and/or within the conductive fluid Fwhich may increase the treatment pulse rate up to the limit of a saferise in tissue temperature—generally local tissue temperature should notbe increased more than about 1 degree C. Heat diffusion on the order of5 mm from the electrodes is required for the heat to be convected byblood circulation. The thermal diffusion time for water at in conduitsof relevant radius range is (5 mm) 2/k=167 seconds. However, a 0.5Jpulse raises a 5 mm radius sphere of water approximately 0.23 degreesC., so a 1-pulse/spark-per-minute rate may be increased to2pulses/sparks-per minute in certain embodiments.

The temperature sensor may be optical fiber based, or amicro-thermocouple. Since saline increases conductivity withtemperature, the current produced by a DC bias applied to the electrodeswill increase monotonically with temperature, allowing the temperatureof the warmest region to be measured directly. As described above, apredetermined heat or temperature increase threshold may be providedwith subsequent alerts and/or corrective or remedial actions implementedby programmed instructions implemented by a processor.

Balloon and Inflation Liquid

Angioplasty balloons are developed and nuanced. Embodiments of thepresent invention comprise standard angioplasty balloons and related,and known, basic inflation/deflation mechanisms. A typical balloonlength may be 12 mm and may be used with 0.14-0.35 in guide wires. Theinflated balloon size may comprise about 90% of the nominal vessel size.

Varying the salinity of the water used to inflate the balloon has animpact on the breakdown voltage between the electrodes similar to theirspacing. Thus, electrode spacing to form a subsonic pressure wavegenerator may be selected to be appropriate for standard saline, or whena lower-than-saline salt concentration used to inflate the balloon, theelectrode spacing may be increased past that used for standard saline.The current density prior to arc formation may be 50A through 0.1 cm²,or about 500A/cm² at 2,000V, so an initial saline concentration shouldbe at least 2.0E-4M NaCl. Standard saline is 0.9% NaCl, or 1.5E-1 M,approximately 1000×more concentrated than required to initiate an arc.

The voltage pulse generated by the pulse generator 300 generatesstreamers in the fluid F interposed between, e.g., the proximal ringelectrode 201 and the next more distal ring electrode 202 that comprisea subsonic pressure wave generator 200. As described above, thedistal-most ring electrode is also operatively connected with the pulsegenerator 300. Sufficient voltage applied to the proximal ring electrode201 results in streamers and ultimately current flowing between the tworing electrodes of the electrode pair 201, 202, generating an arc and aresultant subsonic pressure wave as a bubble forms and expands in thefluid F, and another subsonic pressure wave as the bubble collapses.Generally, the expansion time for the bubble expansion may be measuredin terms of microseconds, e.g., approximately 30 microseconds. Thisexpansion time is slow compared to the transit time of sound across thebubble. “Shock waves” require generation of pressure waves that travelat or greater than the speed of sound.

We note here that this relatively slow expansion time, inter alia,ensures that the pressure wave generated is subsonic. In contrast, anactual shock wave, i.e., traveling at or greater than the speed ofsound, is generated with a much shorter voltage pulse, on the order oftens of nanoseconds.

The distance between ring electrodes of an electrode pair, e.g., 201,202 may be relatively long, e.g., 5 mm or longer. In this case, thegenerated bubble and resulting pressure wave may comprise cylindricalshapes, with the end portions of each more spherical in shape.

The description of the invention and its applications as set forthherein is illustrative and is not intended to limit the scope of theinvention. Features of various embodiments may be combined with otherembodiments within the contemplation of this invention. Variations andmodifications of the embodiments disclosed herein are possible, andpractical alternatives to and equivalents of the various elements of theembodiments would be understood to those of ordinary skill in the artupon study of this patent document. These and other variations andmodifications of the embodiments disclosed herein may be made withoutdeparting from the scope and spirit of the invention.

Having described the invention, we claim:
 1. A method for generating asubsonic pressure wave to a calcified lesion, comprising: providing aballoon catheter comprising: an elongated carrier; a flexible ballooncomprising a material and disposed near a distal end of the elongatedcatheter, wherein a distal end of the flexible balloon is sealed againstthe elongated catheter, the flexible balloon defining an interiorregion; a fluid channel in fluid communication with the interior regionof the flexible balloon and a conductive fluid reservoir, configured toinflate the flexible balloon with the conductive fluid; a proximalelectrode disposed along the elongated carrier and a distal electrodedisposed along the elongated carrier and spaced an axial distance fromthe proximal electrode, the axial distance therebetween comprising aspark gap; and a pulse generator in electrical communication with theproximal electrode, initiating application of a voltage pulse from thepulse generator to one of the proximal electrode or the distalelectrode; causing current to flow between the proximal electrode andthe distal electrode and generating an electrical arc between theproximal electrode and the distal electrode across the spark gap andthrough the conductive fluid; and generating at least one subsonicpressure wave that passes through the conductive fluid and flexibleballoon material at subsonic speed.
 2. The method of claim 1, whereinthe proximal electrode comprises a ring electrode having a front surfaceand a rear surface, wherein the front surface comprises a plurality ofspaced-apart extensions extending away from the front surface and towardthe distal electrode, each spaced-apart extension comprising a length,wherein the plurality of spaced-apart extensions are arrangedcircumferentially spaced-apart around at least part of the front surfaceof the proximal ring electrode; and causing current to flow from one ofthe spaced-apart extensions of the proximal electrode to the distalelectrode; and generating at least one subsonic pressure wave thatpasses through the conductive fluid and flexible balloon material atsubsonic speed.
 3. The method of claim 1, wherein the distal electrodecomprises a ring electrode having a front surface and a rear surface,wherein the front surface comprises a plurality of spaced-apartextensions extending away from the front surface and toward the proximalelectrode, each spaced-apart extension comprising a length, wherein theplurality of spaced-apart extensions are arranged circumferentiallyspaced-apart around at least part of the front surface of the distalring electrode; and causing current to flow from one of the spaced-apartextensions of the distal ring electrode to the proximal electrode; andgenerating at least one subsonic pressure wave that passes through theconductive fluid and flexible balloon material at subsonic speed.
 4. Themethod of claim 2, wherein the distal electrode comprises a ringelectrode having a front surface and a rear surface, wherein the frontsurface comprises a plurality of spaced-apart extensions extending awayfrom the front surface and toward the proximal electrode, eachspaced-apart extension comprising a length, and wherein the plurality ofspaced-apart extensions are arranged circumferentially spaced-apartaround at least part of the front surface of the distal ring electrode;and causing current to flow from one of the spaced-apart extensions ofthe distal ring electrode to one of the spaced-apart extensions of theproximal electrode; and generating at least one subsonic pressure wavethat passes through the conductive fluid and flexible balloon materialat subsonic speed.
 5. The method of claim 3, wherein the proximalelectrode comprises a ring electrode having a front surface and a rearsurface, wherein the front surface comprises a plurality of spaced-apartextensions extending away from the front surface and toward the distalelectrode, each spaced-apart extension comprising a length; and causingcurrent to flow from one of the spaced-apart extensions of the proximalring electrode to one of the spaced-apart extensions of the distalelectrode; and generating at least one subsonic pressure wave thatpasses through the conductive fluid and balloon material at subsonicspeed.
 6. A method for generating a subsonic pressure wave to acalcified lesion, comprising: providing a balloon catheter comprising:an elongated carrier; an angioplasty balloon comprising a material anddisposed near a distal end of the elongated catheter, wherein a distalend of the angioplasty balloon is sealed against the elongated catheter,the angioplasty balloon defining an interior region; a fluid channel influid communication with the interior region of the angioplasty balloonand a conductive fluid reservoir, configured to inflate the balloon withthe conductive fluid; a proximal ring electrode disposed along theelongated carrier and a distal electrode disposed along the elongatedcarrier and spaced an axial distance from the proximal ring electrode,the axial distance therebetween comprising a spark gap; and a pulsegenerator in electrical communication with the proximal ring electrodeand with the distal electrode, wherein the proximal ring electrodecomprises a front surface and a rear surface, wherein the front surfacecomprises a plurality of spaced-apart extensions extending away from thefront surface and toward the distal electrode, each spaced-apartextension comprising a length, and wherein the plurality of spaced-apartextensions are arranged circumferentially spaced-apart around at leastpart of the front surface of the proximal ring electrode; wherein one ofthe spaced-apart extensions comprises a length that is longer than alength of any of the remaining spaced-apart extensions in the plurality;and initiating application of a voltage pulse from the pulse generatorto one of the proximal ring electrode or the distal electrode; causingcurrent to preferentially flow between the longest spaced-apartextension of the proximal ring electrode and the distal electrode; andgenerating at least one subsonic pressure wave that passes through theconductive fluid and flexible balloon material at subsonic speed.
 7. Themethod of claim 6, further comprising causing the current preferentiallyflow from the longest spaced-apart extension of the proximal ringelectrode to the distal electrode.
 8. The method of claim 6, furthercomprising causing the current to preferentially flow from the distalelectrode to the longest spaced-apart extension of the proximal ringelectrode.
 9. A method for generating a subsonic pressure wave to acalcified lesion, comprising: providing a balloon catheter comprising:an elongated carrier; an angioplasty balloon comprising a material anddisposed near a distal end of the elongated catheter, wherein a distalend of the angioplasty balloon is sealed against the elongated catheter,the angioplasty balloon defining an interior region; a fluid channel influid communication with the interior region of the angioplasty balloonand a conductive fluid reservoir, configured to inflate the balloon withthe conductive fluid; a distal ring electrode disposed along theelongated carrier and a proximal electrode disposed along the elongatedcarrier and spaced an axial distance from the distal ring electrode, theaxial distance therebetween comprising a spark gap; and a pulsegenerator in electrical communication with the distal ring electrode andwith the proximal electrode, wherein the distal ring electrode comprisesa front surface and a rear surface, wherein the front surface comprisesa plurality of spaced-apart extensions extending away from the frontsurface and toward the proximal electrode, each spaced-apart extensioncomprising a length and wherein the plurality of spaced-apart extensionsare arranged circumferentially spaced-apart around at least part of thefront surface of the distal ring electrode; wherein one of thespaced-apart extensions comprises a length that is longer than a lengthof any of the remaining spaced-apart extensions in the plurality; andinitiating application of a voltage pulse from the pulse generator toone of the distal ring electrode or the proximal electrode; causingcurrent to preferentially flow between the longest, spaced-apartextension of the distal ring electrode and the proximal electrode; andgenerating at least one subsonic pressure wave that passes through theconductive fluid and balloon material at subsonic speed.
 10. The methodof claim 9, further comprising causing the current to preferentiallyflow from the longest spaced-apart extension of the distal ringelectrode to the proximal electrode.
 11. The method of claim 9, furthercomprising causing the current to preferentially flow from the proximalelectrode to the longest spaced-apart extension of the distal ringelectrode.
 12. The method of claim 9, wherein the proximal electrodecomprises a ring electrode having a front surface and a rear surface,wherein the front surface comprises a plurality of spaced-apartextensions extending away from the front surface and toward the distalelectrode, each spaced-apart extension comprising a length, wherein theplurality of spaced-apart extensions are arranged circumferentiallyspaced-apart around at least part of the front surface of the proximalring electrode; and causing current to flow between the longestspaced-apart, extension of the proximal ring electrode to one of thespaced-apart extensions of the distal electrode; and generating at leastone subsonic pressure wave that passes through the conductive fluid andballoon material at subsonic speed.
 13. The method of claim 12, furthercomprising: causing current to flow from the longest spaced-apartextension of the proximal ring electrode to one of the spaced-apartextensions of the distal electrode; and generating at least one subsonicpressure wave that passes through the conductive fluid and balloonmaterial at subsonic speed.
 14. The method of claim 12, furthercomprising: causing current to flow from the one of the spaced-apartextensions of the distal electrode to the longest spaced-apart extensionof the proximal ring electrode; and generating at least one subsonicpressure wave that passes through the conductive fluid and balloonmaterial at subsonic speed.
 15. The method of claim 12, furthercomprising: causing current to flow from the longest spaced-apartextension of the proximal ring electrode to the longest spaced-apartextension of the distal electrode; and generating at least one subsonicpressure wave that passes through the conductive fluid and balloonmaterial at subsonic speed.
 16. The method of claim 12, furthercomprising: causing current to flow from the longest spaced-apartextensions of the distal ring electrode to the longest spaced-apartextension of the proximal electrode; and generating at least onesubsonic pressure wave that passes through the conductive fluid andballoon material at subsonic speed.
 17. A method for generating asubsonic pressure wave to a calcified lesion, comprising: providing aballoon catheter comprising: an elongated carrier; an angioplastyballoon comprising a material and disposed near a distal end of theelongated catheter, wherein a distal end of the angioplasty balloon issealed against the elongated catheter, the angioplasty balloon definingan interior region; a fluid channel in fluid communication with theinterior region of the angioplasty balloon and a conductive fluidreservoir, configured to inflate the balloon with the conductive fluid;a distal ring electrode disposed along the elongated carrier and aproximal ring electrode disposed along the elongated carrier and spacedan axial distance from the distal ring electrode, the axial distancetherebetween comprising a spark gap; and a pulse generator in electricalcommunication with the distal ring electrode and with the proximalelectrode, initiating application of a voltage pulse from the pulsegenerator to one of the distal ring electrode or the proximal electrode;causing current to preferentially flow between the distal ring electrodeand the proximal ring electrode; and generating at least one subsonicpressure wave that passes through the conductive fluid and balloonmaterial at subsonic speed.
 18. The method of claim 17, furthercomprising: causing the current to flow from the distal ring electrodeto the the proximal ring electrode; and generating at least one subsonicpressure wave that passes through the conductive fluid and balloonmaterial at subsonic speed.
 19. The method of claim 17, furthercomprising: causing the current to preferentially flow from the proximalring electrode to the distal ring electrode; and generating at least onesubsonic pressure wave that passes through the conductive fluid andballoon material at subsonic speed.
 20. A method for generating asubsonic pressure wave to a calcified lesion, comprising: providing aballoon catheter comprising: an elongated carrier; an angioplastyballoon comprising a material and disposed near a distal end of theelongated catheter, wherein a distal end of the angioplasty balloon issealed against the elongated catheter, the angioplasty balloon definingan interior region; a fluid channel in fluid communication with theinterior region of the angioplasty balloon and a conductive fluidreservoir, configured to inflate the balloon with the conductive fluid;a distal ring electrode disposed along the elongated carrier and aproximal ring electrode disposed along the elongated carrier and spacedan axial distance from the distal ring electrode, the axial distancetherebetween comprising a spark gap; and a pulse generator in electricalcommunication with the distal ring electrode and with the proximalelectrode, wherein the distal ring electrode comprises a front surfaceand a rear surface, wherein the front surface comprises a plurality ofspaced-apart extensions extending away from the front surface and towardthe proximal electrode, each spaced-apart extension comprising a length,and wherein the plurality of spaced-apart extensions are arrangedcircumferentially spaced-apart around at least part of the front surfaceof the distal ring electrode; wherein one of the spaced-apart extensionscomprises a length that is longer than a length of any of the remainingspaced-apart extensions in the plurality; wherein the proximal ringelectrode comprises a ring electrode having a front surface and a rearsurface, wherein the front surface comprises a plurality of spaced-apartextensions extending away from the front surface and toward the distalelectrode, each spaced-apart extension comprising a length, wherein theplurality of spaced-apart extensions are arranged circumferentiallyspaced-apart around at least part of the front surface of the proximalring electrode initiating application of a voltage pulse from the pulsegenerator to one of the distal ring electrode or the proximal electrode;causing current to preferentially flow between the longest, spaced-apartextension of the distal ring electrode and the longest, spaced-apartextension of the proximal ring electrode; and generating at least onesubsonic pressure wave that passes through the conductive fluid andballoon material at subsonic speed.
 21. The method of claim 20, furthercomprising causing the current to preferentially flow from the longestspaced-apart extension of the distal ring electrode to the longestspaced-apart extension of the proximal ring electrode; and generating atleast one subsonic pressure wave that passes through the conductivefluid and balloon material at subsonic speed.
 22. The method of claim19, further comprising causing the current to preferentially flow fromthe longest spaced-apart extension of the proximal ring electrode to thelongest spaced-apart extension of the distal ring electrode; andgenerating at least one subsonic pressure wave that passes through theconductive fluid and balloon material at subsonic speed.
 23. A ballooncatheter comprising: an elongated carrier; an angioplasty ballooncomprising a material and disposed near a distal end of the elongatedcatheter, wherein a distal end of the angioplasty balloon is sealedagainst the elongated catheter, the angioplasty balloon defining aninterior region; a fluid channel in fluid communication with theinterior region of the angioplasty balloon and a conductive fluidreservoir, configured to inflate the balloon with the conductive fluid;a proximal ring electrode and a distal ring electrode spaced an axialdistance from the proximal ring electrode, the axial distancetherebetween comprising a spark gap; and a pulse generator in electricalcommunication with the proximal ring electrode, wherein application of avoltage pulse from the pulse generator to the proximal ring electrode isconfigured to generate at least one electrical arc between the proximalring electrode and the distal ring electrode across the spark gap andthrough the conductive fluid, and generation of subsonic pressure wavesthat pass through the conductive fluid and balloon material at subsonicspeed, wherein the proximal ring electrode comprises a front surface anda rear surface, wherein the front surface comprises a plurality ofspaced-apart extensions extending away from the front surface and towardthe distal ring electrode, wherein the plurality of spaced-apartextensions are arranged circumferentially spaced-apart around at leastpart of the front surface of the proximal ring electrode, wherein theplurality of spaced-apart extensions are configured to preferentiallyselect one spaced-apart extension to generate the at least oneelectrical arc across the spark gap.
 24. The balloon catheter of claim23, wherein the preferentially selected first spaced-apart extensioncomprises a length that is longer than the length of any one of theremaining plurality of spaced-apart extensions.
 25. The balloon catheterof claim 24, wherein the preferentially selected spaced-apart extensionof the proximal ring electrode is configured to initiate generation ofthe at least one electrical arc across the spark gap.
 26. The ballooncatheter of claim 24, wherein the preferentially selected spaced-apartextension of the proximal ring electrode is configured to receive the atleast one electrical arc, wherein the at least one electrical arc isinitiated from the distal ring electrode.
 27. A balloon cathetercomprising: an elongated carrier; an angioplasty balloon comprising amaterial and disposed near a distal end of the elongated catheter,wherein a distal end of the angioplasty balloon is sealed against theelongated catheter, the angioplasty balloon defining an interior region;a fluid channel in fluid communication with the interior region of theangioplasty balloon and a conductive fluid reservoir, configured toinflate the balloon with the conductive fluid; a proximal ring electrodeand a distal ring electrode spaced an axial distance from the proximalring electrode, the axial distance therebetween comprising a spark gap;and a pulse generator in electrical communication with the proximal ringelectrode, wherein application of a voltage pulse from the pulsegenerator to the proximal ring electrode is configured to generate atleast one electrical arc between the proximal ring electrode and thedistal ring electrode across the spark gap and through the conductivefluid, and generation of subsonic pressure waves that pass through theconductive fluid and balloon material at subsonic speed, wherein thedistal ring electrode comprises a front surface and a rear surface,wherein the front surface comprises a plurality of spaced-apartextensions extending away from the front surface and toward the proximalring electrode, wherein the plurality of spaced-apart extensions arearranged circumferentially spaced-apart around at least part of thefront surface of the distal ring electrode, wherein the plurality ofspaced-apart extensions are configured to preferentially select onespaced-apart extension in the plurality of spaced-apart extensions togenerate the at least one electrical arc between the proximal ringelectrode and the distal ring electrode.
 28. The balloon catheter ofclaim 27, wherein the preferentially selected spaced-apart extension ofthe distal ring electrode comprises a length that is longer than thelength of any one of the remaining plurality of spaced-apart extensionsof the distal ring electrode.
 29. The balloon catheter of claim 28,wherein the preferentially selected spaced-apart extension of the distalring electrode is configured to initiate generation of the at least oneelectrical arc across the spark gap, wherein the proximal ring electrodeis configured to receive the at least one generated arc.
 30. The ballooncatheter of claim 28, wherein the preferentially selected spaced-apartextension of the distal ring electrode is configured to receive the atleast one generated electrical arc, wherein the at least one electricalarc is initiated by the proximal ring electrode.
 31. A balloon cathetercomprising: an elongated carrier; an angioplasty balloon comprising amaterial and disposed near a distal end of the elongated catheter,wherein a distal end of the angioplasty balloon is sealed against theelongated catheter, the angioplasty balloon defining an interior region;a fluid channel in fluid communication with the interior region of theangioplasty balloon and a conductive fluid reservoir, configured toinflate the balloon with the conductive fluid; a proximal ring electrodeand a distal ring electrode spaced an axial distance from the proximalring electrode, the axial distance therebetween comprising a spark gap;and a pulse generator in electrical communication with the proximal ringelectrode, wherein application of a voltage pulse from the pulsegenerator to the proximal ring electrode is configured to generate atleast one electrical arc between the proximal ring electrode and thedistal ring electrode across the spark gap and through the conductivefluid, and generation of subsonic pressure waves that pass through theconductive fluid and balloon material at subsonic speed, wherein thedistal ring electrode and the proximal ring electrode each comprise afront surface and a rear surface, wherein the front surfaces of thedistal ring electrode and the proximal ring electrode each comprise aplurality of spaced-apart extensions extending away from the frontsurface and toward the spark gap, wherein the plurality of spaced-apartextensions are arranged circumferentially spaced-apart around at leastpart of the front surface of the proximal ring electrode and the distalring electrode, wherein the plurality of spaced-apart extensions of theproximal ring electrode are configured to preferentially select onespaced-apart extension in the plurality of spaced-apart extensions ofthe proximal ring electrode to generate the at least one electrical arc.32. The balloon catheter of claim 31, wherein the preferentiallyselected spaced-apart extension comprises a length that is longer thanthe length of any one of the remaining plurality of spaced-apartextensions of the proximal ring electrode.
 33. The balloon catheter ofclaim 32, wherein the preferentially selected spaced-apart extension ofthe proximal ring electrode is configured to initiate the at least onegenerated electrical arc, wherein the at least one generated arc isreceived by the distal ring electrode.
 34. The balloon catheter of claim32, wherein the preferentially selected spaced-apart extension of theproximal ring electrode is configured to receive the at least onegenerated electrical arc, wherein the at least one generated electricalarc is initiated at the distal ring electrode.
 35. A balloon cathetercomprising: an elongated carrier; an angioplasty balloon comprising amaterial and disposed near a distal end of the elongated catheter,wherein a distal end of the angioplasty balloon is sealed against theelongated catheter, the angioplasty balloon defining an interior region;a fluid channel in fluid communication with the interior region of theangioplasty balloon and a conductive fluid reservoir, configured toinflate the balloon with the conductive fluid; a subsonic pressure wavegenerator disposed along the elongated carrier and within the interiorregion of the balloon and comprising a proximal ring electrode and adistal ring electrode spaced an axial distance from the proximal ringelectrode the axial distance therebetween comprising a spark gap; and apulse generator in electrical communication with the proximal ringelectrode, wherein application of a voltage pulse from the pulsegenerator to the proximal ring electrode is configured to generate atleast one electrical arc between the proximal ring electrode and thedistal ring electrode across the spark gap and through the conductivefluid, and generation of subsonic pressure waves that pass through theconductive fluid and balloon material at subsonic speed, wherein thedistal ring electrode and the proximal ring electrode each comprise afront surface and a rear surface wherein the front surface comprises aplurality of spaced-apart extensions extending away from the frontsurface and toward the spark gap, wherein the plurality of spaced-apartextensions are arranged circumferentially spaced-apart around at leastpart of the front surface of the proximal ring electrode and the distalring electrode, wherein the plurality of spaced-apart extensions of thedistal ring electrode are configured to preferentially select onespaced-apart extension in the plurality of spaced-apart extensions ofthe proximal ring electrode to generate the at least one electrical arc.36. The balloon catheter of claim 35, wherein the preferentiallyselected spaced-apart extension of the distal ring electrode comprises alength that is longer than the length of any one of the remainingplurality of spaced-apart extensions of the distal ring electrode. 37.The balloon catheter of claim 36, wherein the preferentially selectedspaced-apart extension of the distal ring electrode is configured toinitiate the at least one generated electrical arc, wherein the at leastone generated electrical arc is received by the proximal ring electrode.38. The balloon catheter of claim 36, wherein the preferentiallyselected spaced-apart extension of the distal ring electrode isconfigured to receive the at least one generated electrical arc, whereinthe at least one generated electrical arc is initiated by the proximalring electrode.